Membrane lock



FIG. 1 is a top, front, and left side perspective view of an ornamental design for a membrane lock;

FIG. 2 is a top, rear, and left side perspective view of the membrane lock of FIG. 1;

FIG. 3 is a bottom, front, and right side perspective view of the membrane lock of FIG. 1;

FIG. 4 is a top plan view of the membrane lock of FIG. 1;

FIG. 5 is a left side elevational view of the membrane lock of FIG. 1;

FIG. 6 is a front elevational view of the membrane lock of FIG. 1;

FIG. 7 is a right side elevational view of the membrane lock of FIG. 1; and,

FIG. 8 is a rear elevational view of the membrane lock of FIG. 1. 

CLAIM The ornamental design for a membrane lock, as shown and described. 